EP0096445B2

EP0096445B2 - System for maintaining a buoyancy body in position in relation to another body

Info

Publication number: EP0096445B2
Application number: EP83200790A
Authority: EP
Inventors: Leendert Poldervaart
Original assignee: Single Buoy Moorings Inc
Current assignee: Single Buoy Moorings Inc
Priority date: 1982-06-09
Filing date: 1983-06-01
Publication date: 1990-11-28
Anticipated expiration: 2003-06-01
Also published as: IN159039B; BR8303046A; EP0096445A1; US4568295A; ES523132A0; IN160693B; EP0096445B1; NL8202335A; ES8403394A1

Description

The invention relates to a mooring system comprising a vessel, a body such as a buoy, a tower etc., a rigid arm having one end pivotably connected either to the said body or the said vessel, connection means extending vertically between the vessel or the body and that part of the rigid arm extending away from its pivotable connection at either the body or the vessel and a weight which keeps the connection means under tension.
A system of this type is known from e.g. FR-B-2 420 475 in particular Figure 7.
In said known system an arm is used which is pivotably connected to the one body and of which the other end extending deep under waters is connected with the other body by a rod, which other body should be maintained in position in relation to said first mentioned body. A weight is carried by the said rod at the pivotable connection of the arm and the rod. If said last-minute body is moving away from the desired position, then said weight is lifted, the cable suspending said weight will be oriented under an angle in relation to the vertical direction and the magnitude of said angle is determining for the horizontal reset force component derived from said weight, which reset force component should function for bringing the drifting body back in position. In most cases a tanker has to be kept at a distance from a mooring buoy. The buoy and the tanker can be exposed to heavy movements and in this known system therefore the weight is positioned at a large depth underneath the bottom of the ship to take care that the weight is not touching the ship, not even in the situation in which the ship is moving towards said buoy.
Because of the large length of the rod carrying said weight, the dislocation of the ship should be relatively large to create a reset force component, which is able to oppose the disturbing forces and to bring the ship notwithstanding the great mass thereof back in position. Therefore said known system functions as a soft spring.
In the published European patent EP-A-0096446 in the name of the same applicant filed on the same day as the above-mentioned application, it is already proposed to position the point of attachment of the arm with the weight biased connection means or cable at a higher level to convert said soft spring into a stiff spring. However, the weight thereby still remains at a large depth.
The object of the invention is now not only to eliminate the disadvantage of the soft spring, but also to transfer the weight from the position deep under water to another place.
Said object is reached by the invention in that the weight is attached to the rigid arm the point of attachment of the connection means to the arm is remote from and above the level of the bottom of said vessel, near the water surface.
According to the invention the body can be a buoy, a tower, a riser or any other member.
In all cases the arm or arms which preferably extend even above water level can form a connection upon which noses or conduit swivel can easily be reached and maintained or repaired.
In case two arms are used said arms preferably are connected to the body by means of universal joints and near the ends turned away from the body are interconnected transversely by a connecting member which has been connected with the arms in a flexible way. By doing this the arms are kept spaced apart whilst transfer of movements of the vessel towards the body are reduced to a minimum.
In all embodiments the arm or arms can have water ballast spaces. Dueto this a mooring system is possible having arm or arms which in emptied condition of the ballast spaces have buoyancy which allows easy connection with the vessel. Filling said ballast spaces with water then creates the weight from which the return force component may be derived.
It is observed that from the US patent specification 3,155,069 a buoy is known having a bifurcated arm rigidly connected thereto and rotatable about a vertical arm, which arm carries a weight. The ends of said arm are by means of mooring cables connected to said weight which is swayable around a horizontal axis. Thereby, however, said weight does not have any effect through said arm and through the mooring cables onto the ship, but only through said bow cable.
The invention will be explained in more detail with reference to the drawings.

Figure 1 illustrates schematically a side-view of the principle onto which the invention is based.
Figure 2 is a side-view of a further embodiment and
Figure 3 is the corresponding top-view.
Figure 4 is a side-view of a further embodiment and
Figure 5 is the thereto corresponding top-view.
Figure 6 is a top-view of another embodiment.

Figure 1 illustrates a fixed positioned body 1, such as a quay ortower, and a thereto moored ship 2. Said ship is kept at a distance from the quay 1 by means of one or more arms 3, of which one end is at 4 pivotable around a horizontal axis, attached to the quay 1 and of which the other end 5 is pivotable attached to a connection means 6, which may have the form of a cable, a chain or rod, the upper end 7 of which connection means is pivotably attached to the ship 2. A weight 8 is positioned onto said arm or arms under which influence in the connection means 6 a tensile force is created from which reset force component is derived in case the ship 2 is dislocated in relation to the quay 1.
In the embodiment of Figure 2 and 3 a normal buoy 21 is used fastened to anchor chains 22 and carrying a turntable 23. Arms 26 and 27 are attached to said turntable through spherical pivot joints or flexible joints, i.e. joints which have at least a horizontal pivot shaft, and which are indicated by 24 and 25, and the ends 28, 29 of said arms are again through a connection means 30 carried by the ship 2.
Eventually a flexible distance element 31 can be installed between said arms.
The arms 26, 27 carry weights 32, 33 which eventually may be embodied as cylinders, which are dislocatable in length direction.
In the embodiment of Figures 4 and 5 a buoy 34 is used fastened by means of anchor chains 35 and carrying a turntable 36 integrated to the arm 37, which is bifurcated in both ends 38 and 39, suspended through the connection means 40 respectively 41 from the ship. Said arm 37 may be embodied as a hollow arm with a ballast space 42 and if necessary an additional weight 43 can be installed onto said arm.
The embodiment of Figure 6 illustrates a buoy comprising of two buoyancy bodies 44, 45 with a connecting element 46 installed inbetween together with the turntable 47 for the anchor chains 48. The ends of said arms 44, 45 are also in this case attached to the ship 2 through connection means 49, 50. Said arms comprise ballast spaces 51, 52 for generating the reset forces.

Claims

1. Mooring system comprising a vessel (2), a body (1, 21, 34, 46) such as a buoy, a tower etc., a rigid arm (3, 26, 27, 37, 44, 45) having one end pivotably connected either to the said body of the said vessel connection means (6, 30, 40, 49, 50) extending vertically between the vessel (2) or the body and that part of the rigid arm extending away from its pivotable connection at either the body or the vessel and a weight (8, 32, 33, 43, 51, 52) which keeps the connection means (6, 30, 40, 49, 50) under tension, characterized in that the weight is attached to the rigid arm (3, 26, 27, 37, 44,45) the point of attachment (5,12,13,28,29) of the connection means (6,30,40,49,50) to the arm (3,26,27,37,44,45) is remote from and above the level of the bottom of said vessel (2) near the water surface.

2. Mooring system as claimed in claim 1, characterized in that the said body (1, 9, 21, 34, 46) is a buoy anchored by means of anchor chains which are connected to an anchor chain turntable (19) which turntable is supported by the rigid arm (10, 11) at a location between the ends of said arm (10, 11) whilst the weight is formed by the anchor chains (20).

3. Mooring system as claimed in claim 2, characterized in that the buoy is a cylindrical body (9) with a horizontal longitudinal axis extending in the same direction as the arms (10, 11).

4. Mooring system as claimed in claim 2, characterized in that the buoy comprises two cylindrical bodies (9) extending parallel to each other and each having a rigid arm (10, 11) rigidly connected to said bodies respectively.

5. Mooring system as claimed in claim 1, characterized in that two arms extend between the body and the vessel arm having a universal joint (24, 25) at its point of connection with the body (21) which arms near the ends which are turned away from the body are interconnected by a transverse connecting member (31) the outer ends of which are connected to said arms in a flexible way.

6. Mooring system according to one or more of the preceding claims, characterized in that the arm or arms (37, 44, 45) are provided with ballast water spaces (42, 51, 52).